There are eight diastereomers of 1,2,3,4,5,6 -hexachlorocyclohexane. Draw each in its more stabl

There are eight diastereomers of 1,2,3,4,5,6...

Key Concepts

Diastereomerism

Diastereomerism refers to stereoisomers that are not mirror images of each other. These isomers differ in configuration at one or more stereogenic centers, which leads to differences in their physical and chemical properties. In the context of substituted cyclohexanes, the spatial arrangement of substituents on the ring creates multiple diastereomeric forms with distinct reactivities and stabilities.

Cyclohexane Chair Conformations

Cyclohexane predominantly adopts a chair conformation to minimize angle and torsional strain. In this conformation, substituents can occupy either axial or equatorial positions. Equatorial positions generally provide greater stability because they reduce steric interactions, whereas axial positions are more prone to 1,3-diaxial interactions. Understanding these conformations is crucial when analyzing the reactivity of substituents on a cyclohexane ring.

Axial vs Equatorial Substitution

The position of substituents on a cyclohexane ring, whether axial or equatorial, greatly affects their chemical reactivity. Axial substituents are oriented perpendicular to the ring plane and are involved in steric clashes, while equatorial substituents extend outward and experience less hindrance. In elimination reactions, an axial leaving group is often necessary to achieve the proper geometry for the reaction to proceed efficiently.

E2 Reaction Mechanism

The E2 (bimolecular elimination) reaction is a single-step process where a base abstracts a proton and the leaving group departs simultaneously, resulting in the formation of a double bond. For an E2 reaction to occur efficiently, the hydrogen to be abstracted and the leaving group must be aligned in an anti-periplanar fashion. This alignment ensures optimal orbital overlap, which is critical for the reaction to proceed.

Anti-Periplanar Geometry

Anti-periplanar geometry is a stereoelectronic requirement in the E2 elimination mechanism. It involves the leaving group and the hydrogen being removed being positioned opposite each other on adjacent carbon atoms in the same plane. In substituted cyclohexanes, only substituents in axial positions typically fulfill this geometric criterion, thereby influencing the rate of the reaction.

Transcript

00:01 So we have 1, 2, 3, 4, 5, 6, hexaclorocyclohexane, and the question asks us to draw each of its 8 diasteremermers.

00:10 So for the sake of orientation, you'll see here in the top right how i'm going to number each position.

00:17 The top right position is going to be one, and going kind of clockwise, it's going to progress, so 2, 3, 4, 5, 6.

00:24 And so we can go ahead and start drawing our diosteromers.

00:27 There's a systematic way that i like doing it.

00:29 So i like drawing the most stable chair confirmation first.

00:34 And of course, that's going to be where all of our cyc, i'm sorry, all of our chloro groups are going to be equatorial to each other.

00:40 So i'm going to say that we're going to have, in other words, zero axial chlorides.

00:46 So why don't we go ahead and draw that to look like the following, where we have zero axiuclides.

00:56 And although there are hydrogens, i'm not going to draw them just because the problem will get very messy.

01:02 But just know that they're there.

01:11 All right.

01:13 So this is going to be our first diasteremer, where we have zero axial chlorides.

01:18 And now our next diastairmer is going to contain one axial chloride.

01:23 So i'm just going to put that our axial chloride in the one position because that's the easiest to see.

01:29 We can draw it in the two position, three position four, five, six, whatever.

01:32 It's going to be the same molecule just rotated.

01:35 So why don't we go ahead and draw that? all right.

01:42 So our one position.

01:43 Chloride here, it's going to be axial, and then all the rest are going to remain equatorial.

01:54 All right.

01:56 So now i'm going to draw our next diasteremermer where we have two axial chlorides, and we're going to have a couple of those.

02:04 So let's say we have two axial chlorides, one in the one position and one in the two position.

02:10 So we can go ahead and draw that diastereumer.

02:17 So now we have axial in the one position and axial in the two position.

02:23 Then the the remaining are equatorial.

02:31 And now we can go systematically.

02:33 What if we draw our axial chlorides in the one and three positions? so that'll be our next diastereumer.

02:44 Right.

02:45 So axial 1 and axial 3.

02:50 That's going to be drawn up here.

02:53 And now the rest are going to be equatorial.

03:01 Right? that's our next diastereumer.

03:04 And now systematically we would think 1 4, our axiocloride in the one in four positions.

03:11 However, oh yeah, yeah...

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